High frequency switch and mobile communication equipment

ABSTRACT

A high frequency switch, has 
     a transmitting terminal; 
     a receiving terminal; 
     an antenna terminal; 
     a first diode having an anode electrically connected to the transmitting terminal and a cathode electrically connected to the antenna terminal; 
     a second diode having an anode connected through a transmission line of ¼ wavelength to the antenna terminal which is electrically connected to the receiving terminal, and having the side of a cathode grounded; and 
     a control terminal provided to a node between the transmitting terminal and the first anode, 
     wherein the first and second diodes have a tradeoff relationship between ON resistance thereof and capacitance between the anode and the cathode, and 
     the ON resistance of the first diode is lower than the ON resistance of the second diode, and the capacitance of the second diode in the OFF state is smaller than the capacitance of the first diode in the OFF state.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high frequency switch or the like, ofwhich main object is to switch a high frequency signal in a radiocircuit of radio communication equipment such as a portable telephone.

2. Description of the Prior Art

High frequency switch circuits are often used to switch transmit/receivesignals in radio circuits of radio communication equipment such as aportable telephone using TDMA systems.

Hereinafter, an example of conventional high frequency switch circuitsdescribed above will be described with reference to a drawing.

FIG. 13 shows an equivalent circuit diagram of an example ofconventional high frequency switch circuits.

In FIG. 13, the anode of a first diode D1301 is coupled to atransmitting terminal 1301 through a first capacitor element C1301.Further, a control terminal 1302 is coupled to the anode side of thefirst diode D1301 through an inductor element L1301 and a resistorelement R1301. Also, the anode of a second diode D1302 is coupled to areceiving terminal 1303 through a second capacitor element C1302, andthe cathode of the second diode is connected to ground. Further, one endof a first transmission line TL1301, which has an electrical length of ¼wavelength at the operating frequency, is connected also to the anodeside of the second diode D1302. The other end of the first transmissionline is connected to the cathode of the first diode D1301, and alsocoupled to an antenna terminal 1304 through a third capacitor elementC1303. Here, in order to decrease the variety of components to be usedand thereby to reduce cost, usually, diodes having the samecharacteristics are used for the first diode D1301 and the second diodeD1302.

The operation of the high frequency circuit configured as describedabove will be described.

In transmitting, when a positive voltage is applied to the controlterminal 1302, the first diode D1301 and the second diode D1302 areturned on. At this time, the capacitor elements C1301, C1302, and C1303block components of direct current. A transmit signal passes through thecapacitor C1301 from the transmitting terminal 1301 and is transmittedto the antenna terminal 1304 through the first diode D1301 and thecapacitor element C1303. Herein, the transmission line TL1301 operatesas a ¼ wavelength resonator having one end grounded, because the seconddiode D1302 is turned on. Therefore, the impedance of lines in the sideof the antenna terminal 1304 becomes infinite and therefore no transmitsignal is transmitted to the receiving side.

In receiving, no voltage is applied to the control terminal 1302, andtherefore both the first diode D1301 and the second diode D1302 are inthe OFF state. Thus, a receive signal is transmitted to the receivingterminal 1303 from the antenna terminal 1304 through the capacitorelement C1303, the transmission line TL1301, and the capacitor elementC1302.

PIN diodes are mainly used for the first diode D1301 and the seconddiode D1302, which are used for switching. However, generally, diodeshave a tradeoff relationship that a diode of low ON resistance has alarge capacitance between the cathode and anode terminals and a diodehaving a small inter-terminal capacitance in the OFF state has a high ONresistance.

Therefore, if importance is attached on isolation during receiving andtherefore a diode having a small inter-terminal capacitance is selectedto achieve high isolation, the signal path produces a large loss duringtransmitting because of the large ON resistance of the diode.

On the other hand, when importance is attached on insertion loss duringtransmitting and therefore a diode of a low ON resistance is selected,then there is a problem that the increased inter-terminal capacitancereduces isolation to result in a large loss produced by the signal pathduring receiving.

BRIEF SUMMARY OF THE INVENTION

The present invention has been achieved in view of such problems, andhas an object to provide a high frequency switch favorably reducing lossproduced in signal paths both during transmitting and during receiving.

One aspect of the present invention is a high frequency switch,comprising:

a transmitting terminal;

a receiving terminal;

an antenna terminal;

a first diode having an anode electrically connected to saidtransmitting terminal and a cathode electrically connected to saidantenna terminal;

a second diode having an anode connected through a transmission line of¼ wavelength to the antenna terminal which is electrically connected tosaid receiving terminal, and having the side of a cathode grounded; and

a control terminal provided to a node between said transmitting terminaland said first anode,

wherein said first and second diodes have a tradeoff relationshipbetween ON resistance thereof and capacitance between said anode andsaid cathode, and

the ON resistance of the first diode is lower than the ON resistance ofthe second diode, and the capacitance of the second diode in the OFFstate is smaller than the capacitance of the first diode in the OFFstate.

Another aspect of the present invention is the high-frequency switch,

wherein a diode having a ON resistance of not higher than 1Ω is used forsaid first diode and a diode having an inter-terminal capacitance of notlarger than 0.8 pF in the OFF state is used for said second diode.

Still another aspect of the present invention is the high frequencyswitch,

wherein a diode having a ON resistance of not higher than 0.8Ω is usedfor said first diode and a diode having an inter-terminal capacitance ofnot larger than 0.5 pF in the OFF state is for said second diode.

Yet still another aspect of the present invention is the high frequencyswitch,

Still yet another aspect of the present invention is the high frequencyswitch, further comprising a capacitor element or a parallel circuit ofLC connected in series with said second diode.

A further aspect of the present invention is a high frequency switch,comprising:

a laminated component having a plurality of dielectrics laminatedtherein;

a transmitting terminal, a receiving terminal, an antenna terminal, acontrol terminal, a ground terminal, and an electrode pattern forconnecting a part, which are provided on the surface of said laminatedcomponent;

a first diode having an anode electrically connected to saidtransmitting terminal and having a cathode electrically connected tosaid antenna terminal; and

a second diode having an anode connected through a transmission terminalof ¼ wavelength to the antenna terminal which is electrically connectedto said receiving terminal, and having the side of a cathode grounded,said first and second diodes being mounted on the surface of saidlaminated component,

wherein said first and second diodes have a tradeoff relationshipbetween ON resistance thereof and capacitance between said anode andsaid cathode, and

the ON resistance of the first diode is lower than the ON resistance ofthe second diode, and the capacitance of the second diode in the OFFstate is smaller than the capacitance of the first diode in the OFFstate.

A still further aspect of the present invention is the high frequencyswitch,

wherein said high frequency switch is configured by using the laminatedcomponent.

A yet further aspect of the present invention is a two-band type of highfrequency switch, comprising:

a second high frequency switch for use in a second frequency band higherthan the first frequency band; and

a divider for sharing the same antenna between said first high frequencyswitch and said second high frequency switch by multiplexing anddemultiplexing said first frequency band and second frequency band, theantenna terminal of said first high frequency switch and the antennaterminal of said second high frequency switch being electricallyconnected to each other,

wherein the high frequency switch is used for said first high frequencyswitch and said second high frequency switch.

A still yet further aspect of the present invention is the two-band typeof high frequency switch,

wherein the ON resistance of said first diode of said second highfrequency switch is made lower than the ON resistance of said firstdiode of said first high frequency switch, and

the capacitance of said second diode, in the OFF state, of said secondhigh frequency switch is made smaller the capacitance of said seconddiode, in the OFF state, of said first high frequency switch.

An additional aspect of the present invention is the two-band type ofhigh frequency switch,

wherein the ON resistance of said first diode of said first highfrequency switch is not higher than 1Ω and the ON resistance of saidfirst diode of said second high frequency switch is not higher than0.8Ω, and

the capacitance of said second diode, in the OFF state, of said firsthigh frequency switch is not larger than 0.8 pF, and the capacitance ofsaid second diode, in the OFF state, of said second high frequencyswitch is not larger than 0.5 pF.

A still additional aspect of the present invention is the two-band typeof high frequency switch,

wherein a transmitting terminal, a receiving terminal, and a controlterminal of said first high frequency switch, a transmitting terminal, areceiving terminal, and a control terminal of said second high frequencyswitch, and the antenna terminal common to said first high frequencyswitch and said second high frequency switch are provided on the surfaceof a laminated component having a plurality of dielectrics laminatedtherein, along with a ground terminal as electrode patterns forconnecting parts, and said first high frequency switch, said second highfrequency switch, and said divider are provided in the interior of saidlaminated component, and said first diode and said second diode aremounted on the surface of said laminated component.

A yet additional aspect of the present invention is a three-band type ofhigh frequency switch, comprising:

a second high frequency switch for use in a second frequency band higherthan the first frequency band;

a third high frequency switch for use in a third frequency band higherthan the first frequency band;

a divider for sharing the same antenna among said first high frequencyswitch, said second high frequency switch, and said third high frequencyswitch, by multiplexing and demultiplexing said first frequency band,said second frequency band and said third frequency band, the antennaterminal of said first high frequency switch and the antenna terminal ofsaid second high frequency switch being electrically connected to eachother,

wherein the high frequency switch is used for said first high frequencyswitch and said second high frequency switch, and

said third high frequency switch has a third diode having a cathodeconnected to between said antenna terminal and a node of the cathode ofsaid first diode and said transmission line and having an anodeconnected to a second receiving terminal, and a second control terminalconnected to between said third diode and said second receivingterminal,

said third high frequency switch using the transmitting terminal of saidfirst high frequency switch as a second transmitting terminal thereof,and said third high frequency switch operating on the receiving side, byusing said second diode of said second high frequency switch.

A still yet additional aspect of the present invention is the three-bandtype of high frequency switch,

wherein the ON resistance of said first diode of said second highfrequency switch and said third diode of said third high frequencyswitch are made lower than the ON resistance of said first diode of saidfirst high frequency switch, and

the capacitance of said second diode, in the OFF state, of said secondhigh frequency switch is made smaller than the capacitance of saidsecond diode, in the OFF state, of said first high frequency switch.

A supplementary aspect of the present invention is the three-band typeof high frequency switch,

wherein the ON resistance of said third diode of said third highfrequency switch is lower than the ON resistance of said first diode ofsaid second high frequency switch.

A still supplementary aspect of the present invention is the three-bandtype of high frequency switch,

wherein the ON resistance of said first diode of said first highfrequency switch is not higher than 1Ω and the ON resistance of saidfirst diode of said second high frequency switch and said third diode ofsaid third high frequency switch is not higher than 0.8Ω, and

the capacitance of said second diode, in the OFF state, of said firsthigh frequency switch is not larger than 0.8 pF, and the capacitance ofsaid second diode, in the OFF state, of said second high frequencyswitch is not larger than 0.5 pF.

A yet supplementary aspect of the present invention is the three-bandtype of high frequency switch,

wherein the ON resistance of said third diode of said third highfrequency switch is made not higher than 0.5 Ω.

A still yet supplementary aspect of the present invention is thethree-band type of high frequency switch,

wherein the transmitting terminal, receiving terminal, and controlterminal of said first high frequency switch, the transmitting terminal,receiving terminal, and control terminal of said second high frequencyswitch, the receiving terminal and control terminal of said third highfrequency switch, and the antenna terminal common to said first highfrequency switch, said second high frequency switch, and said third highfrequency switch are provided on the surface of a laminated componenthaving a plurality of dielectrics laminated therein, along with a groundterminal as electrode patterns for connecting parts, and

electrode patterns for configuring said first high frequency switch,said second high frequency switch, said third high frequency switch, andsaid divider are provided in the interior of said laminated component,and said first diode, said second diode, and said third diode aremounted on the surface of said laminated component.

Another aspect of the present invention is radio communicationequipment, comprising:

an antenna;

transmitting means for transmitting a signal from said antenna;

receiving means for receiving a signal from said antenna; and

switch means for switching the connection between said antenna and saidtransmitting means or said receiving means,

wherein the high frequency switch is used for said switch means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a circuit diagram of a high frequency switch circuitaccording to an embodiment 1 of the present invention;

FIG. 2 shows a mounting diagram of the embodiment 1 of the presentinvention;

FIG. 3 shows a perspective diagram of a lamination type of highfrequency switch according to an embodiment 2 of the present invention;

FIG. 4 shows an exploded perspective diagram of the lamination type ofhigh frequency switch according to the embodiment 2 of the presentinvention;

FIG. 5 shows a circuit diagram of the embodiment 2 of the presentinvention;

FIG. 6 shows a circuit diagram of an embodiment 3 of the presentinvention;

FIG. 7 shows a circuit diagram of an embodiment 4 of the presentinvention;

FIG. 8 shows examples of the characteristics of PIN diodes;

FIG. 9 shows a circuit diagram of an embodiment 5 of the presentinvention;

FIG. 10 shows an example of the transmission characteristics of adivider;

FIG. 11 shows a circuit diagram of an embodiment 6 of the presentinvention;

FIG. 12 shows a block circuit diagram of radio communication equipmentimplementing the high frequency switch circuit according to the presentinvention; and

FIG. 13 shows a circuit diagram of an example of a conventional highfrequency switch circuit.

DESCRIPTION OF SYMBOLS

111, 201, 301, 401, 501, 601, 701, 801, 811, 1101, 1111, 1301 . . .Transmitting terminal

112, 202, 302, 402, 502, 602, 702, 802, 812, 1102, 1112, 1302 . . .Control terminal

113, 203, 303, 403, 503, 603, 703, 803, 813, 1103, 1113, 1123, 1303 . .. Receiving terminal

114, 204, 304, 404, 504, 604, 704, 804, 814, 1104, 1114, 1304 . . .Antenna terminal

C . . . Capacitor element

D . . . Diode

G . . . Ground electrode

L . . . Inductor element

R . . . Resistor element

TL . . . Transmission line

V . . . Via electrode

300, 400 . . . Laminated component

400A, 400B, 400C, 400D . . . Dielectric sheet

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

Hereinafter, a high frequency switch circuit according to the embodiment1 of the present invention will be described with reference to a circuitfor use in switching of an antenna, which is often used to carry outcommunication in TDMA systems. FIG. 1 shows an equivalent circuit of ahigh frequency switch circuit according to the embodiment 1. In FIG. 1,an anode of a first diode D101 is coupled to a transmitting terminal 101through a first capacitor C101. Further, a control terminal 102 iscoupled to an anode side of the first diode D101 through an inductorelement L101 and a resistor element R101. An anode of a second diodeD102 is coupled to a receiving terminal 103 through a second capacitorelement C102, and a cathode of the second diode is connected to ground.

One end of a transmission line TL101 having an electrical length of ¼wavelength at an operating frequency is connected also to the anode sideof the second diode D102, and the other end of the transmission line isconnected to the cathode of the first diode D101 and also coupled to theantenna terminal 104 through a third capacitor element C103. Herein, anON resistance of the first diode D101 is lower than that of the seconddiode D102, and the capacitance of the second diode D102 in the OFFstate is smaller than that of the first diode D101 in the OFF state.

The operation of the high frequency switch circuit configured asdescribed above will be described.

In the case of transmitting, when a positive voltage is applied to acontrol terminal 102, the first diode D101 and the second diode D102 areturned on. At this time, the capacitance elements C101, C102, and C103block components of direct current and thus no current flows to therespective terminals. Also, the inductor element L101 is used as a highfrequency choke to prevent a high frequency current from flowing to thecontrol terminal 102. Also, the resistance element R101 is used to feeda bias current through the diode D101 and D102.

A transmit signal transmitted from the transmitting terminal 101 passesthrough the capacitor element C101 and the first diode D101 and then istransmitted to the antenna terminal 104 through the capacitor elementC103. At this time, the transmission line TL101 acts as aone-end-grounded resonator, because the second diode D101 is turned onso as to ground the transmission line TL101. Therefore, the impedance ofthe transmission line on the side of the antenna is nearly infinite toisolate the receiving side at high frequencies, thereby the transmitsignal being not transmitted to the receiving side. Because a diode oflow ON resistance is used for the first diode D101, the signal linecarrying the transmit signal is made a path of low loss.

Next, in the case of receiving, no voltage is applied to the controlterminal 102 and therefore the first diode D101 and the second diodeD102 are in the OFF state. A receive signal passes through the capacitorelement C103 from the antenna terminal 104, and then is transmitted tothe receiving terminal 103 through the transmission line TL101 and thecapacitor element C102. Herein, because a diode having a smallinter-terminal capacitance in the OFF state is used for the second diodeD102, the second diode can offer a high degree of isolation, therebycausing the receive signal to be transmitted to the receiving terminal103 without leakage to the ground side, to which the second diode D102is connected. Therefore, the signal path carrying the receive signal ismade a path of low loss.

FIG. 2 is a top view of an example of a printed circuit board having thecircuit of FIG. 1 formed thereon. A printed circuit board P201 is madeof a glass fabric based epoxy resin or the like, and provided with aground electrode on the back side thereof not shown. Transmission linesTL201 to TL205 are micro-strip lines formed on the printed circuit boardP201. An inductor element L201 realized with an air core coil, capacitorelements C201 to C203 realized with chip capacitors or the like, aresistor element R201 realized with a chip resistor or the like, a firstdiode D201, and a second diode D202 all are mounted on the printedcircuit board P201 by soldering or the like. Reference character G201denotes an electrode provided for grounding the cathode side of thesecond diode D202, and the electrode is electrically connected through athrough-hole to the ground electrode on the back side of the printedcircuit board P201. The printed circuit board P201 is provided with atransmitting terminal 201, a control terminal 202, a receiving terminal203, and an antenna terminal 204.

As described above, in the present embodiment, a diode of low ONresistance is used for the diode on the transmitting side, and a diodehaving a small inter-terminal capacitance in the OFF state is used forthe diode on the receiving side. As a result, in either case oftransmitting and receiving, the signal path carrying a transmit signalor a receive signal can realize a high frequency switch circuit of lowloss.

Embodiment 2

Next, an embodiment 2 of the present invention will be described withreference to drawings. FIGS. 3, 4 and 5 are respectively a perspectiveview, an exploded perspective view and a circuit diagram of a laminatedcomponent configuring a high frequency switch circuit according to theembodiment 2 of the present invention. In FIG. 3, terminal electrodesfor a transmitting terminal 301, an ground terminal 302, a receivingterminal 303, an ground terminal 304, an antenna terminal 305, and acontrol terminal 306 are provided on the sides and on the top and bottomsurfaces, near to the sides, of the laminated component 300 having aplurality of dielectric sheets laminated therein. Electrodes 307, 308,309, 310, 311, and 312 are electrodes provided on the surface of thelaminated component 300.

A first diode D301 and a second diode D302 are respectively connected tothe electrodes 310 and 312 and to the electrodes 302 and 311 bysoldering or the like. In the same manner, an inductor element L301 anda resistor element R301 are connected to the electrodes 307 and 308 andto the electrodes 308 and 309, respectively.

FIG. 4 is an exploded perspective view of the high frequency switch ofFIG. 3. Terminal electrodes for a transmitting terminal 401, a groundterminal 402, a receiving terminal 403, a ground terminal 404, anantenna terminal 405, and a control terminal 406 are provided on thesides and on the top and bottom surfaces, near to the sides, ofdielectric sheets 400A, 400B, 400C, and 400D. Electrode patterns 407,408, 409, 410, 411, and 412 are provided on the top surface of thedielectric sheet 400A. A transmission line TL401 extending from thetransmitting terminal 401 is provided on the dielectric sheet 400B, andelectrically connected to the electrode pattern 407 through a via V401,which is used for supplying a control voltage. The transmission lineTL401 is also connected to the electrode pattern 410 through a via 402.

The sheet TL402 provided on the dielectric sheet 400C extends from theantenna 405 to the receiving terminal 403 and is further electricallyconnected to the electrode patterns 411 and 412 through vias V403 andV404, respectively. Aground electrode G401 provided on the sheet 400D isgrounded through the ground terminal 402 and the control terminal 406.

An example of the configuration of the laminated component shown in FIG.4 comprises circuit elements enclosed in the dotted line shown in thecircuit diagram of FIG. 5. Further, capacitor elements C501, C502 andC503 for blocking direct currents are provided on a wiring boardequipped with this laminated component, thus configuring a highfrequency switch circuit module.

By the way, in the embodiment shown in FIG. 3, the resistor R301 andinductor element L301 have been described as discrete components mountedon the surface of the laminated component 300. However, the laminatedcomponent 300 can contain the resistor element and the inductor elementas a printed resistor and as a transmission line of high impedance,respectively, thereby providing the same advantages.

Further, in FIG. 5, although the capacitor elements C501, C502, and C503are respectively provided for the transmitting terminal 501, receivingterminal 503, and antenna terminal 504 as external elements of thelaminated component 300, these elements can be also contained in thelaminated component 300, providing the same advantages. In such manners,by making the laminated component contain each element configuring thehigh frequency switch, the switch can be made smaller, and further morereliable.

Embodiment 3

Next, an embodiment 3 of the present invention will be described withreference to a drawing. FIG. 6 shows an equivalent circuit of a highfrequency switch circuit according to the embodiment 3 of the presentinvention. A difference from the embodiment 1 is in that a seriescircuit of a capacitor element C604 and an inductor element L602 isprovided in parallel with a first diode D601. This is for increasing theisolation between an antenna terminal 604 and a transmitting terminal601 during receiving by using the inter-terminal capacitance of thefirst diode D601 in the OFF state and the inductor element L602.

Herein, the capacitor element 604 is provided in order to block acomponent of direct current from a control terminal 602, and has such alarge value of capacitance as to avoid resonance in the frequency bandto be used by the first diode in the ON state.

Thereby, the high frequency switch circuit according to the embodimentcan realize a reduction in loss produced in the path of transmit signalsduring transmitting, and also realize an increased isolation of thesignal path on the transmitting side during receiving, thus providing ahigher-performance switch circuit.

By the way, although the above embodiment has been described as beingprovided with the series circuit of the capacitor element C604 and theinductor element L602, a single inductor element may be used instead ofthe series circuit.

Embodiment 4

Next, an embodiment 4 of the present invention will be described withreference to drawings. FIG. 7 shows an equivalent circuit diagram of ahigh frequency switch circuit according to the embodiment 4 of thepresent invention. A difference from the embodiment 3 is in that aparallel circuit of an inductor element L703 and a capacitor elementC705 is provided in series with a second diode D702, in addition to theembodiment 3. This parallel circuit is provided for the purpose ofreducing the grounding resistance during transmitting by establishingseries resonance between an inter-terminal inductor component of thesecond diode D702 in the ON state and the capacitor element C705.

Thereby, the embodiment provides a high frequency switch circuit inwhich the signal path during transmitting has lower loss and higherisolation than the embodiment 3.

FIG. 8 shows an example of the characteristics showing the relationshipbetween the ON resistance and the inter-terminal capacitance of PINdiodes. As shown in this figure, a PIN diode of lower ON resistance hasa larger inter-terminal capacitance, and a PIN diode of smallerinter-terminal capacitance has a higher ON resistance. The first diodepreferably has an ON resistance of not higher than 1Ω, more preferablynot higher than 0.8Ω. Also, the second diode in the OFF state has aninter-terminal capacitance of not higher than 0.8 pF, more preferablynot higher than 0.5 pF. Further, this relationship between the firstdiode and the second diode is also the same for the embodiments 1 to 3.

Further, the above embodiments has been described as being provided withthe parallel circuit of the capacitor element C705 and the inductorelement L703, but a single capacitor element may be used instead of theparallel circuit.

Also, the above embodiment has been described as the addition of theparallel circuit of the capacitor element C705 and the inductor elementL703 to the configuration of the embodiment 3, but the parallel circuitmay be added to the configuration of the embodiment 1.

Embodiment 5

FIG. 9 shows the equivalent circuit diagram of a two-band type of highfrequency switch circuit implementing the high frequency switch circuitaccording to the present invention. The two-band type of high frequencyswitch circuit according to this embodiment has the two switches of afirst high frequency switch 900A for use in a first frequency band f1and a second high frequency switch 900B for use in a second frequencyband f2 higher than the first frequency band. Further, respectiveantenna terminals 904 and 914 for each of the high frequency switchesare combined together in a divider 920 so as to be coupled to an antennaterminal 930. Thus, the two high frequency switches share the sameantenna, which is connected to the antenna terminal 930, not shown.

Hereinafter, the two-band type of high frequency switch according to theembodiment 5 of the present invention will be described taking GSM andDCS systems used in mobile communication in Europe as specific examples.Herein, f1 is assumed to be a band of 880 to 960 MHz, which is thefrequency band for transmitting/receiving in the GSM system, and f2 isassumed to be a band of 1710 to 1880 MHz, which is the frequency bandfor transmitting/receiving in the DCS system. Further, herein, thefollowing description will use an example of the divider 920 which isconfigured with a low pass filter and a high pass filter each having therespective characteristics as shown in FIG. 10. In addition to this, thedivider 920 may be also configured by combining two kinds of band passfilters each having different pass bands.

In transmitting, applying a voltage to a control terminal 902 of thefirst high frequency switch 900A turns on diodes D901 and D902, andtherefore a transmit signal of the GSM band passes through a capacitorelement C901, a diode D901, and a capacitor element C903 from atransmitting terminal 901, then inputting to a terminal 904 on the sideof a low pass filter (LPF) of the divider 920.

Applying a voltage to a control terminal 912 of the second highfrequency switch 900B turns on diodes D911 and 912, and therefore atransmit signal of the DCS band passes through a capacitor element C911,a diode D911, and a capacitor element C913 from a transmitting terminal911, then inputting to a terminal 914 on the side of a high pass filter(HPF) of the divider 920. Each of the transmit signals input to thedivider 920 is output to the antenna terminal 930 without being outputto another side of the high frequency switches, because isolation isprovided in the cross band as shown in FIG. 9.

In receiving, when the control terminal is turned off, a signal receivedat the antenna is input from the antenna terminal 930 to the diplexer920. Then, the signal is output to the antenna terminal 904 of the LPFside if the signal is of the GSM band and to the antenna terminal 914 ofthe HPF side if the signal is of the DCS band by the diplexer 920,respectively.

A signal of the GSM band passes through the capacitor element C903, atransmission line TL901, and a capacitor element C902 from the antennaterminal 904, and then is output to a receiving terminal 903 for the GSMband. Further, a signal of the DCS band passes through the capacitorelement C913, a transmission line TL911, and a capacitor element C912from the antenna terminal 914, and then is output to a receivingterminal 913 for the DCS band.

In such a configuration, in both of the first high frequency switch 900Aand the second high frequency switch 900B, the first diodes D901 andD911 placed on the side of the transmitting terminals 901 and 911 areprovided with lower ON resistance than the second diodes D902 and D12placed on the side of the receiving terminals 903 and 913. Further, thediodes D902 and D912 placed on the side of the receiving terminals 903and 913 are provided with smaller inter-terminal capacitance in the OFFstate than the diodes D901 and D911 placed on the side of thetransmitting terminals. As a result, the embodiment provides the samelow-loss high frequency switch as in the case of the embodiment 1, thatis, the two-band high frequency switch of low loss is provided. In thiscase, preferably, the ON resistance of the diode D901 is not higher than1Ω, and that of the diode D911 is not higher than 0.8Ω, and also theinter-terminal capacitance of the diode D902 is not larger than 0.8 pF,and that of the diode D912 is not larger than 0.5 pF.

The configuration as described above realizes, in the lower frequencyside, an increase in isolation during receiving, thus reducing leakagesignals to the transmitting-terminal side, though a little large loss isproduced on the transmitting side. Further, because high frequencyswitches is generally desired to be lower in loss in the higherfrequency side during transmitting, the ON resistance is made small. Byusing such two-band type of high frequency switch, it is possible toreduce power consumption of radio communication equipment.

Further, the diplexer 930 used in this configuration permits variousoperations according to requirements of communication systems, such astransmitting and receiving of two waves, or receiving duringtransmitting at one side.

Embodiment 6

FIG. 11 shows a three-band type of high frequency switch circuitimplementing the high frequency switch circuit according to the presentinvention. The three-band type of high frequency switch circuitaccording to the embodiment has the three switches of a first highfrequency switch 1100A for use in a first frequency band f1, a secondhigh frequency switch 1000B for use in a second frequency band f2 higherthan the first frequency band, and a third high frequency switch 1100Cfor use in a third frequency band f3 higher than the first frequencyband. Further, respective antenna terminals 1104 and 1114 of each highfrequency switch are combined together in a diplexer so as to be coupledto an antenna terminal 1130. Thus, the three high frequency switchesshare the same antenna not shown.

Further, the first high frequency switch 1100A and the second highfrequency switch 1100B respectively have the same configuration as thehigh frequency switch of the embodiment 1.

Further, the third high frequency switch 1000C shares, as theconfiguration of the transmitting side thereof, a transmitting terminal1111, a capacitor element C1111, an inductor element L1111, a resistorelement R1111, a control terminal 1112, and a first diode D1111 with thesecond high frequency switch 1100B. The third high frequency switch1110C also shares an antenna terminal 1114 forming a signal path forboth a transmit signal and a receive signal, and a capacitor elementC1113 with the second high frequency switch 1100B. The third highfrequency switch 1110C further shares, as a part of the configuration ofthe receiving side thereof, a transmission line TL1111 and a seconddiode D1112 with the second high frequency switch 1110B.

Further, the receiving side of the third high frequency switch 1100Ccomprises a third diode D1121 having an anode connected between acapacitor element D1113 and a node of the first diode D1111 and thetransmission line TL1111 and having a cathode coupled to a receivingterminal 1123 through a capacitor element C1122, a control terminal 1122coupled to a node of the anode of the third diode D1121 and thecapacitor element C1122 through a series circuit of a resistor elementR1121 and an inductor element L1122, and a series circuit of a capacitorelement C1121 and an inductor element L1121, which series circuit isconnected in parallel with the third diode D1121.

That is, the third high frequency switch has a receiving circuit havingthe third diode D1121 and a peripheral circuit, a transmitting circuithas the first diode D1111 and a peripheral circuit and a switchingcircuit having the second diode D1112 and the transmission line TL1111.Furthermore, the transmission circuit is shared with the second circuit1000B in flowing of high frequency signal and the switching circuit isshared with the second circuit 1100B in flowing of direct current.

Hereinafter, the three-band type of high frequency switch according toan embodiment 6 of the present invention will be described taking GSMand DCS systems used in mobile communication in Europe and PCS systemsused in USA as specific examples. Herein, f1 is assumed to be a band of880 to 960 MHz, which is the frequency band for transmitting/receivingin the GSM system, f2 is assumed to be a band of 1711 to 1880 MHz, whichis the frequency band for transmitting/receiving in the DSC system, andf3 is assumed to be a band of 1860 to 1990, which is the frequency bandfor transmitting/receiving in the PCS system.

In transmitting, applying a voltage to a control terminal 1102 of thefirst high frequency switch 1100A turns on a first diode D1101 and asecond diode D1102, and therefore a transmit signal of the GSM bandinput to a transmitting terminal 1101 is supplied through a capacitorelement C1101, the first diode D1101, and a capacitor element C1103 toan antenna terminal 1104 on the side of a low pass filter (LPF) of thedivider 1120.

Applying a voltage to a control terminal 1112 of the second highfrequency switch 1100B (the third high frequency switch 1100C) turns ondiodes D1111 and D1112, and therefore transmit signals of the DCS bandand PCS band are supplied from a transmitting terminal 1111 to theterminal 1114 of a high pass filter (HPF) of the divider 1130 throughthe capacitor element C1111, the first diode D1111, and the capacitorelement C1113.

Because the divider 1120 is provided with isolation in the cross band asshown in FIG. 9 referred to in the embodiment 5, each transmit signalinput to the divider 1120 is output to the antenna terminal 1130 withoutbeing output to the side of the different high frequency switch.

In receiving, when the control terminals 1102, 1112 and 1122, are turnedoff, a signal of the GSM band received at the antenna and input from theantenna terminal 1130 to the divider 1120 is output to the antennaterminal 1104 of the LPF side by the divider 1120. Also, in the samemanner, signals of the DCS and PCS bands are output to the antennaterminal 1114 of the HPF side.

A signal of the GSM band passes through the capacitor element C1103, atransmission line TL1101, and a capacitor element C1102 from the antennaterminal 1104, and then is output to a receiving terminal 1103 for theGSM band.

Also, a signal of the DCS band passes through a capacitor element C1113,a transmission line TL1111, and a capacitor element C1112 from theterminal 1114, and then is output to a receiving terminal 1113 for theDCS band.

Further, in the receiving of a signal of the PCS band, when a voltage isapplied to the control terminal 1122, the third diode D1121 and thesecond diode D1112 are turned on for an operation of the third highfrequency switch 1100C. Thus, a receive signal of the PCS band is outputfrom the antenna terminal 1114 to the receiving terminal 1123 for thePCS band through the capacitor element C1113, the third diode D1121, andthe capacitor element C1122.

Further, when the third diode D1121 is turned off, that is, when thethird diode D1121 operates as part of the second high frequency switch1110B to receive a DCS band signal, the inter-terminal capacitance ofthe third diode D1121 and the inductor element L1121 produce a parallelresonance, thereby ensuring isolation between the DCS band and PCS bandso as to prevent the signal of the DCS band from flowing to the side ofthe receiving terminal 1123 for the PCS.

In such a configuration, the first diodes D1101 and D1111 each placed onthe side of the receiving terminals 1101 and 1111 and the third diodeD1121 for use in receiving signals of the PCS band are provided withlower On resistance than the second diodes D1102 and D1112 each placedon the side of the receiving terminals 1103 and 1113. Further, thesecond diodes D1102 and D1112 placed on the side of the receivingterminals 1103 and 1113 are provided with smaller inter-terminalcapacitance in the OFF state than the diodes D1101 and D1111 placed onthe side of the transmitting terminals 1101 and 1111. As a result, thisconfiguration provides a low-loss high frequency switch.

Further, the diodes used in the second high frequency switch 1100B andthe third high frequency switch 1100C, which operate on the side ofhigher frequency, are desirably selected to make the switches lower inloss than the first high frequency switch 1100A operating on the side oflower frequency. Further, the ON resistance of the third diode D1121 isdesirably lower than the ON resistance of the first diode D1101 on theside of the transmitting terminal 1101 in the first high frequencyswitch 1100A.

For example, in this case, desirably, the ON resistance of the firstdiode D1101 is not higher than 1Ω, the ON resistance of the first diodeD1111 is not higher than 0.8Ω, the ON resistance of the third diodeD1121 is not higher than 0.5Ω, and the inter-terminal capacitance of thesecond diodes D1102 and D1112 in the OFF state each are not higher than0.8 pF.

By using the three-band type of high frequency switch having the aboveconfiguration, a diode of low ON resistance is used for receivingsignals of the PCS system, thus permitting low loss, and the inductorelement connected in parallel with the diode D1121 permits sufficientisolation.

Further, in the other circuit portions of the above configuration, thecharacteristics of the same low-loss and high isolation as the two-bandtype of high frequency switch are obtained. Using the three-band type ofhigh frequency switch having such a configuration permits a reduction inpower consumption of radio communication equipment because of thereduced loss of the transmitting side. Further, the divider used in theconfiguration permits independent operations such as transmitting andreceiving at the same time on the side of GSM and the side of DCS andPCS as in the case of the two-band type of high frequency switch.Furthermore, making up the above configuration into a laminatedstructure can realize a smaller three-band type high frequency switch,and thus permits smaller radio communication equipment.

Embodiment 7

FIG. 12 shows a block diagram of the radio portion of radiocommunication equipment mounting the high frequency switch circuitaccording to the present invention. When a voltage is applied to acontrol terminal 1201, a first diode D1201 and a second diode D1202 areturned on, and therefore a transmit signal from a power amplifier PApasses through a capacitor element C1201, a diode element D1201, and acapacitor element C1203 from a transmitting terminal 1211, and then istransmitted from an antenna 1210. Herein, the power amplifier PAconfigures the means of the present invention along with an oscillatorOSC, a mixer MIX, and a band pass filter BPF.

Also, when a voltage is not applied to the control terminal 1201, thefirst diode D1201 and the second diode D1202 are turned off, andtherefore a receive signal from the antenna 1210 passes through thecapacitor element 1203, a transmission line TL1201, and a capacitorelement C1201, and inputs to a low noise amplifier LNA via a receivingterminal 1212. Herein, the low noise amplifier LNA configures receivingmeans of the present invention along with the oscillator OSC, a mixerMIX, and a band pass filter BPF on the receiving side.

In transmitting, because of the low ON resistance of the first diodeD1201, the transmit signal from the power amplifier PA can betransmitted with a little loss. Further, the transmit signal is nottransmitted to the receiving terminal because one end of thetransmission line TL1201 is grounded. In receiving, because the seconddiode D1202 has a small inter-terminal capacitance in the OFF state, areceive signal can be transmitted to the low noise amplifier LNA withoutattenuation.

In the embodiment 2, although the circuit of the embodiment 1 has beenrealized in the laminated component, the circuits of the embodiments 3,4, 5, and 6 can be also realized in the laminated component. Further,the transmission lines in the laminated component have been formed inone layer, but a multi-structure having 2 or more layers of transmissionlines can provide the same advantages.

As described above, the present invention can provide a high frequencyswitch of low-loss and high isolation. Further, a laminated structure ofthe high frequency switch can be used to make the switch smaller andhigher reliable, thereby permitting smaller size and reducedpower-consumption of radio communication equipment.

What is claimed is:
 1. A high frequency switch, comprising: atransmitting terminal; a receiving terminal; an antenna terminal; afirst diode having an anode electrically connected to said transmittingterminal and a cathode electrically connected to said antenna terminal;a second diode having an anode connected through a transmission line of¼ wavelength to the antenna terminal which is electrically connected tosaid receiving terminal, and having the side of a cathode grounded; anda control terminal provided to a node between said transmitting terminaland said first anode, wherein said first and second diodes have atradeoff relationship between ON resistance thereof and capacitancebetween said anode and said cathode, and the ON resistance of the firstdiode is lower than the ON resistance of the second diode, and thecapacitance of the second diode in the OFF state is smaller than thecapacitance of the first diode in the OFF state.
 2. The high frequencyswitch according to claim 1, wherein a diode having a ON resistance ofnot higher than 1Ω is used for said first diode and a diode having aninter-terminal capacitance of not larger than 0.8 pF in the OFF state isused for said second diode.
 3. The high frequency switch according toclaim 1, wherein a diode having a ON resistance of not higher than 0.8Ωis used for said first diode and a diode having an inter-terminalcapacitance of not larger than 0.5 pF in the OFF state is for saidsecond diode.
 4. The high frequency switch according to any one ofclaims from 1 to 3, further comprising an inductor element or a seriescircuit of LC connected in parallel with said first diode.
 5. The highfrequency switch according to any one of claims from 1 to 3, furthercomprising a capacitor element or a parallel circuit of LC connected inseries with said second diode.
 6. Radio communication equipment,comprising: an antenna; transmitting means for transmitting a signalfrom said antenna; receiving means for receiving a signal from saidantenna; and switch means for switching the connection between saidantenna and said transmitting means or said receiving means, wherein thehigh frequency switch according to any one of claims 1 to 3 is used forsaid switch means.